1. Field of the Invention
The present invention relates to a phase-change memory cell and a method of fabricating the memory cell and, more particularly, to a phase-change memory cell and a method of fabricating the memory cell in which a stencil layer is used to form a phase-change material layer.
2. Description of the Related Art
Nonvolatile memory elements based on the phase-change properties of the chalcogenide materials has a long history dating back to the '70s. Most known implementations of chalcogenide-based random access memory cells use the chalcogenide element both for read-out (based on its resistance change between the crystalline and amorphous state) and for write (based on Joule heating when current is passed through the chalcogenide).
The resistivity of chalcogenide can vary over a very wide range from nearly insulating to fairly conducting. This could sometimes be useful during film deposition to create a different initial resistive state of the chalcogenide material formed from the subsequent cyclable states used for memory operatoin, so as to encourage the formation of high-current density filamentary conduction paths within the memory element for better time-response. In such cases often a “break-in” procedure is necessary for each chalcogenide cell to condition it such that it is stable for repeated current-induction of thermal cycling between the crystalline and amorphous states This procedure, plus the reliability problems associated with a large drive current passing through the chalcogenide for writing (large enough to cause a temperature swing of up to 600° C. degree locally involving current densities on the order of 106 A/cm2 through the chalcogenide), makes large-scale adoption of the phase-change mechanism for memory difficult.
These are two of the key issues facing the application of the chalcogenide-type of phase-change memories in mass-produced circuits. Specifically, the issues include reliability associated with large current density through the chalcogenide element, and the need to individually break-in each chalcogenide element for reproducible operation.